The continuing objectives of this research are to elucidate factors which participate in the regulation of intestinal growth and differentiation, and to delineate the regulatory steps at which regulators (or modulators) exert their effects. We propose to use hypophysectomized-artifically reared (HAR) rat pups as an in vivo system to examine hormonal effects on gastric emptying rate, intestinal villus length, crypt depth and epithelial cell proliferation. Autoradiographic techniques will be used to determine cell migration rates. At the same time, intestinal disaccharidase activites will be measured, and the intracellular synthesis, and transport of sucrase-isomaltase will be examined by a comination of biochemical, immunocytochemical and autoradiographic techniques. The realtive effects of hormonal therapy systemic and luminal routes will be determined. To evaluate separately the effects of luminal and systemic factors on intestinal growth, we plan to use an in vivo - in vitro system. The intestine of newborn rats will be transplanted into the subcutaneous layer of syngeneic littermates. Differences in cell proliferation after hormonal therapy between implanted and host intestine will permit us to distinguish luminal factors from systemic factors. We also propose to use primary cultures as an in vitro system to (1) develop optimal conditions for both cell proliferation and phenotype maintenance; (2) determine hormonal effects on cell proliferation and differentiation and (3) examine hormonal effects on the differentiation of specialized intestinal cell types. Attempts will also be made to subculture and propagate epithelial cells. The effect of hydrocortisone and thyroxin on cell proliferation will be examined by flow cytometry. The effect of these hormones on the expression of the sucrase-isomaltase will be determined.